Belt winder for a vehicle occupant seat belt

ABSTRACT

A belt retractor for a vehicle occupant seat belt, comprising a belt reel ( 14 ) rotatably mounted in a housing ( 12 ), a torsion bar ( 21 ) extending in the interior of said belt reel ( 14 ) and connected by its first axial end ( 22 ) non-rotatably to said belt reel ( 14 ) and by its second axial end ( 26 ) non-rotatably to a ratchet disk ( 18 ) provided with a ratchet toothing ( 16 ), and a load-bearing ratchet pawl ( 42 ) capable of being brought into engagement with said ratchet toothing ( 16 ) to block said belt reel ( 14 ), is characterized in that said torsion bar comprises a first section ( 28 ) as well as a second section ( 30 ), the cross-section of which is smaller than that of said first section ( 28 ), that an arresting portion ( 24 ) is configured between said first and second sections ( 28, 30 ) and that a bypass element ( 34 ) is provided which can be transposed from a starting position connecting said arresting portion ( 24 ) non-rotatably to said second end ( 26 ) of said torsion bar ( 21 ) into a release position in which said arresting portion ( 24 ) is rotatable relative to said second axial end ( 26 ) of said torsion bar.

The invention relates to a belt retractor for a vehicle occupant seatbelt, comprising a belt reel rotatably mounted in a housing, a torsionbar extending in the interior of the belt reel and connected by itsfirst axial end non-rotatably to the belt reel and by its second axialend non-rotatably to a ratchet disk provided with a ratchet toothing,and a load-bearing ratchet pawl capable of being brought into engagementwith the ratchet toothing to block the belt reel.

The torsion bar in the interior of the belt reel serves to limit themaximum force acting in the seat belt, especially when the vehicle isinvolved in an accident, to a degree preventing injury of a restrainedvehicle occupant. Limiting the force is achieved in that as of acritical belt webbing force, rotation of the belt reel relative to thenon-rotatably mounted ratchet disk is made possible, as a result ofwhich a specific length of the belt webbing can be dispensed from thebelt reel. This dispensed length of belt webbing is available as anadditional length for decelerating, more particularly, the trunk of thevehicle occupant.

As regards the trunk, the risk of injury for a vehicle occupant isdictated almost exclusively by the force acting as a whole on the trunk.If only the seat belt is used to restrain the vehicle occupant, theforce acting on the trunk results exclusively from the force in the beltwebbing. If, however, a gas bag is additionally used, which is deployedin front of the vehicle occupant when the vehicle is involved in anaccident, to ensure a controlled deceleration of the vehicle occupant,the load on the trunk as of a specific forward dislocation is composedof the force introduced into the trunk by the seat belt as well as theforce introduced into the trunk by the gas bag. So that the overall loadacting on the trunk does not exceed a predetermined degree, it would bedesirable for the force acting in the seat belt to decrease as of thatpoint in time at which the trunk of the vehicle occupant comes intocontact with the gas bag. Preferably, the change in the forcecounteracting dispensing of the belt webbing should be brought about byas simple means as possible, it being further desirable that thecharacteristic of the belt webbing force versus released belt webbinglength is freely adjustable within broad limits so that the beltretractor can be adapted to the individual mounting conditions in thevehicle.

The invention provides a belt retractor satisfying these requirements.In accordance with the invention it is provided for in the case of abelt retractor of the kind as stated at the outset that the torsion barcomprises a first section as well as a second section, the cross-sectionof which is smaller than that of the first section, that an arrestingportion is configured between the first and second sections and that abypass element is provided which can be transposed from a startingposition connecting the arresting portion non-rotatably to the secondend of the torsion bar into a release position in which the arrestingportion is rotatable relative to the second axial end of the torsionbar. In this configuration, release of the belt webbing occurs initiallyonly with twisting of the first section of the torsion bar; the secondsection of the torsion bar is not involved in twisting since it isbypassed by the bypass element. Depending on the respective mountingsituation, the bypass element is transposed, following a predeterminedrotation of the belt reel relative to the ratchet disk, from thestarting position into the release position. At this point, also thesecond section of the torsion bar is involved in the rotation of thebelt reel relative to the ratchet disk. Since the second section has asmaller cross-section. than the first section, a lesser belt webbingdispensing force is needed. The point in time of transposing the bypasselement from the starting position into the release position ispreferably selected such that it coincides with the start of the divingaction of the trunk of the vehicle occupant into the deployed gas bag.

In accordance with a preferred embodiment it is provided for that thearresting portion and the second axial end of the torsion bar aresplined and that the bypass element is a bypass sleeve splinedcomplementary in its interior. In this embodiment the bypass element isconfigured as a sleeve which is particularly simple to fabricate,slidingly arranged on the arresting portion and on the second axial endof the torsion bar. For transposing the bypass sleeve from the startingposition into the release position, a variety of mechanisms of simpledesign may be provided. For example, a positioning cylinder may beemployed which is activated by means of a pyrotechnic charge.Preferably, however, the bypass element is transposed from the startingposition into the release position mechanically.

In accordance with a preferred embodiment it is furthermore provided forthat the first axial end of the torsion bar is also splined and that apositioning sleeve is arranged non-rotatably on the first axial end ofthe torsion bar, this positioning sleeve being splined complementary inits interior and comprising an end face facing the second axial end ofthe torsion bar, which end face is configured as a control cam withwhich the end face of the bypass sleeve facing the first axial end ofthe torsion bar is in contact. In this configuration a rotation of thearresting portion relative to the first axial end of the torsion bar isdirectly exploited to transpose the bypass sleeve from the startingposition into the release position. By suitably configuring the controlcam it can be set as of which rotation of the first axial end of thetorsion bar relative to the arresting portion the second section of thetorsion bar is involved in the rotation of the belt reel. A limitationexists only to the extent that the release position needs to be attainedat the latest after one revolution of the arresting portion relative tothe first axial end of the torsion bar.

If more than one revolution of the belt reel is desired before also thesecond section of the torsion bar is involved in limiting the force, athread may be configured, for example, on the bypass sleeve in which acounterpiece engages such that a transposition of the bypass sleeve fromthe starting position into the release position is possible. Dependingon the pitch of the thread, the point in time at which the bypass sleeveis transposed into the release position can be set to any desired degreeof relative rotation between the arresting portion and the first axialend of the torsion bar.

Advantageous aspects of the invention read from the sub-claims.

The invention will now be described below with reference to a preferredembodiment as illustrated in the drawings in which:

FIG. 1 is a schematic view of a belt retractor for a vehicle occupantseat belt;

FIG. 2 is a schematic cross-sectional view of a belt reel including atorsion bar for a belt retractor in accordance with the invention;

FIG. 3 is an illustration of the developed shape of a positioning sleeveas may be used in the belt retractor in accordance with the invention;

FIG. 4 is an illustration of the developed shape of a bypass sleeve asmay be used in the belt retractor in accordance with the invention, and;

FIG. 5 is a plot of the belt webbing dispensing force versus time for aconventional belt retractor and a belt retractor in accordance with theinvention.

Referring now to FIG. 1 there is illustrated in perspective a beltretractor in accordance with the invention. The belt retractor 10contains a housing 12 in which a belt reel 14 is rotatably mounted.Provided at one axial end of the belt reel 14 is a ratchet disk 18.Configured on the outer circumference of the ratchet disk 18 is aratchet toothing 16 into which a ratchet pawl (not shown) can be causedto engage. A seat belt 20 can be wound on the belt reel 14.

Referring now to FIG. 2 there is illustrated the schematic cross-sectionof the belt reel 14 with the ratchet disk 18. Located in the interior ofthe belt reel is a torsion bar 21 consisting of a first axial end 22, anarresting portion 24, a second axial end 26 as well as a first section28 between the first axial end 22 and the arresting portion 24 and asecond section 30 between the arresting portion 24 and the second axialend 26. The second section 30 of the torsion bar has a smallercross-section than the first section 28. The first axial end 22, thesecond axial end 26 as well as the arresting portion 24 of the torsionbar are splined.

The first axial end 22 of the torsion bar is non-rotatably connected tothe belt reel 14 by means of the spline. The second axial end 26 of thetorsion bar is non-rotatably connected to the ratchet disk 18.

Also arranged in the interior of the belt reel are a positioning sleeve32 and a bypass sleeve 34. The developed shapes of these two sleeves areillustrated in FIGS. 3 and 4. The positioning sleeve 32 is splined onthe inside, complementary to the spline of the first axial end 22 of thetorsion bar, and is mounted on the first axial end 22 of the torsion barsuch that it is non-rotatably connected thereto whilst being in contactwith the face wall of the belt reel 14. The axial end of the positioningsleeve 32 facing the second axial end 26 of the torsion bar extends sofar towards the second axial end 26 of the torsion bar to be just out ofcontact with the arresting portion 24. The end face of the positioningsleeve 32 facing the second axial end 26 of the torsion bar isconfigured as a control cam 40.

The inner side of the bypass sleeve 34 is also splined complementary tothat of the arresting portion 24 and of the second axial end 26. In thestarting position as shown in FIG. 2 the axial end of the bypass sleeve34—shown on the left in FIG. 2—is arranged non-rotatably on thearresting portion 24 whilst the axial end of the bypass sleeve 34 shownon the right in FIG. 2—is arranged non-rotatably on the second axial end26 of the torsion bar. The end face 44 of the bypass sleeve 34 facingthe first axial end 22 of the torsion bar is in contact with the controlcam 40 of the positioning sleeve 32.

When, in the starting position of the bypass sleeve 34, the ratchet pawl42 indicated schematically in FIG. 2 is caused to engage the ratchettoothing 16 of the ratchet wheel 18, then the second axial end 26 of thetorsion bar is initially blocked via the ratchet wheel 18. Due to thehigh moment of torsional resistance made available by the bypass sleeve34, the arresting portion 24 is also coupled non-rotatably to the secondaxial end 26 of the torsion bar; the second portion 30 receiving(practically) no load whatsoever. If now, with the ratchet wheel 18blocked, a load is applied to the belt reel 14 by means of the beltwebbing 20, this initially results in only the first section 28 of thetorsion bar being twisted. This torsion comes along with the bypasssleeve 34 being rotated relative to the positioning sleeve 32 since thepositioning sleeve 32 is connected non-rotatably to the first axial end22 whilst the bypass sleeve 34 rotates together with the second axialend 26 and the arresting portion 24 of the torsion bar. During thisrotation, the end face 44 of the bypass sleeve 34 facing the first axialend 22 of the torsion bar is shifted to the right in the direction ofthe arrows P as evident from FIG. 2 by the control cam 40 of thepositioning sleeve 32. With increasing rotation of the first axial end22 relative to the arresting portion 24 of the torsion bar, the bypasssleeve 34 is shifted so far to the right that it no longer engages thespline of the arresting portion 24. This position, in which a rotationof the arresting portion 24 relative to the second axial end 26 of thetorsion bar is possible, is termed the release position. So that theuncoupling action of the arresting portion 24 from the bypass sleeve 34occurs smoothly, the spline on the inner side of the bypass sleeve 34 isconfigured only over a portion which has the same axial length over thefull inner circumference; i.e. no spline being provided in a portion 46beyond this axial length.

The control cam 40 as shown in FIG. 3, together with the complementaryend face area 44 as shown in FIG. 4 for the bypass sleeve 34, is merelyone example of how the positioning sleeve 32 and the bypass sleeve 34may be configured. The control cam may also be provided with a larger oreven smaller pitch, it being possible, for example, to obtain thecontrol cam by performing a slanting cut through the sleeve providedwith the spline on the inner side, i.e. at an angle other than 90°relative to the longitudinal axis of the sleeve. Important in thisrespect is merely that, following one revolution of the arrestingportion 24 relative to the first axial end 22 of the torsion bar at thelatest, such an axial shift is made available by the control cam 40 thatthe bypass sleeve 34 is transposed from the starting position into therelease position.

Referring now to FIG. 5 there is illustrated a plot of the belt webbingdispensing force F versus time t for a typical head-on collision of avehicle. The bold line curve 1 represents the profile for a conventionalbelt retractor including a force limiter. It is evident that thedispensing force of the belt webbing firstly increases sharply beforeincreasing slightly. The broken line curve 2 illustrates the profile ofthe belt webbing dispensing force for a belt retractor in accordancewith the invention. It is evident that up to a point in time t_(k) thecurves 1 and 2 run parallel. As of the point in time t_(k), however, areduction in the belt webbing dispensing force occurs in the case of thebelt retractor in accordance with the invention. The time t_(k)represents the point in time at which the bypass sleeve 34 is decoupledfrom the arresting portion 24, so that in addition to the first section28 also the second section 30 of the torsion bar is involved in thetwisting action. Since the cross-section of the second section 30 issmaller than that of the first section 28, a reduction in the beltwebbing dispensing force takes place. The point in time t_(k)corresponds precisely to the point in time at which the vehicle occupantdives into the deployed gas bag. The decrease in the belt webbingdispensing force at this point in time assures that the overall load onthe trunk of the vehicle occupant remains more or less constant.

What is claimed is:
 1. A belt retractor for a vehicle occupant seatbelt, comprising a belt reel (14) rotatably mounted in a housing (12), atorsion bar (21) extending in the interior of said belt reel (14) andconnected by its first axial end (22) non-rotatably to said belt reel(14) and by its second axial end (26) non-rotatably to a ratchet disk(18), and comprising a ratchet toothing (16) as well as a load-bearingratchet pawl (42) in engagement with said ratchet toothing (16) to blocksaid belt reel (14), said torsion bar having a first section (28) aswell as a second section (30), the cross-section of which is smallerthan that of said first section (28), an arresting portion (24) beingconfigured between said first and second sections (28, 30) and a bypasselement (34) being provided which is transposed from a starting positionbridging said second section of said torsion bar into a release positionin which said second section of said torsion bar is released,characterized in that a positioning sleeve (32) is arrangednon-rotatably on said first axial end of said torsion bar, saidpositioning sleeve comprising an end face facing said second axial end(26) of said torsion bar, which end face is configured as a control cam(40) with which the end face (44) of said bypass sleeve (34) facing saidfirst axial end (22) of said torsion bar is in contact.
 2. The beltretractor as set forth in claim 1, characterized in that said controlcam (40) is configured such that, after a predetermined rotation of saidarresting portion (24) relative to said first axial end (26) of saidtorsion bar, said bypass sleeve (34) is shifted toward said second axialend (26) of said torsion bar to such an extent that said arrestingportion (24) no longer engages said bypass sleeve (34).
 3. The beltretractor as set forth in claim 1, characterized in that said firstaxial end (22) of said torsion bar is splined and that said positioningsleeve (32) is splined complementary in its interior.
 4. The beltretractor as set forth in claim 1, characterized in that said arrestingportion (24) and said second axial end (26) of said torsion bar aresplined and that said bypass element is a bypass sleeve (34) splinedcomplementary in its interior.
 5. A belt retractor for a vehicleoccupant seat belt, comprising a belt reel (14) rotatably mounted in ahousing (12), a torsion bar (21) extending in the interior of said beltreel (14) and connected by its first axial end (22) non-rotatably tosaid belt reel (14) and by its second axial end (26) non-rotatably to aratchet disk (18), and comprising a ratchet toothing (16) as well as aload-bearing ratchet pawl (42) in engagement with said ratchet toothing(16) to block said belt reel (14), said torsion bar having a firstsection (28) as well as a second section (30), the cross-section ofwhich is smaller than that of said first section (28), an arrestingportion (24) being configured between said first and second sections(28, 30) and a bypass element (34) being provided which is transposedfrom a starting position bridging said second section of said torsionbar into a release position in which said second section of said torsionbar is released, characterized in that an end face is configured on saidbypass sleeve (34) which is engaged by a cam to move said bypass sleeve(34) from said starting position into said release position.
 6. A beltretractor for a vehicle occupant seat belt, comprising a belt reel (14)rotatably mounted in a housing (12), a torsion bar (21) extending in theinterior of said belt reel (14) and connected by its first axial end(22) non-rotatably to said belt reel (14) and by its second axial end(26) non-rotatably to a ratchet disk (18) provided with a ratchettoothing (16), and a load-bearing ratchet pawl (42) in engagement withsaid ratchet toothing (16) to block said belt reel (14), characterizedin that said torsion bar comprises a first section (28) as well as asecond section (30), the cross-section of which is smaller than that ofsaid first section (28), that an arresting portion (24) is configuredbetween said first and second sections (28, 30) and that a bypasselement (34) is provided which is transposed from a starting positionconnecting said arresting portion (24) non-rotatably to said second end(26) of said torsion bar (21) into a release position in which saidarresting portion (24) is rotatable relative to said second axial end(26) of said torsion bar, characterized in that said arresting portion(24) and said second axial end (26) of said torsion bar are splined andthat said bypass element is a bypass sleeve (34) splined complementaryin its interior, characterized in that said first axial end (22) of saidtorsion bar is also splined and that a positioning sleeve (32) isarranged non-rotatably on said first axial end of said torsion bar, saidpositioning sleeve being splined complementary in its interior andcomprising an end face facing said second axial end (26) of said torsionbar, which end face is configured as a control cam (40) with which anend face (44) of said bypass sleeve (34) facing said first axial end(22) of said torsion bar is in contact.
 7. The belt retractor as setforth in claim 6, characterized in that said control cam (40) isconfigured such that, after a predetermined rotation of said arrestingportion (24) relative to said first axial end (26) of said torsion bar,said bypass sleeve (34) is shifted toward said second axial end (26) ofsaid torsion bar to such an extent that said arresting portion (24) nolonger engages said bypass sleeve (34).